• Structural Engineering and Mechanics
• /
• 제56권2호
• /
• pp.169-188
• /
• 2015

There are two types of nonlinear analysis methods for building frameworks depending on the method of modeling the plastification of members including lumped plasticity and distributed plasticity. The lumped plasticity method assumes that plasticity is concentrated at a zero-length plastic hinge section at the ends of the elements. The distributed plasticity method discretizes the structural members into many line segments, and further subdivides the cross-section of each segment into a number of finite elements. When a reinforced concrete member experiences inelastic deformations, cracks tend to spread form the joint interface resulting in a curvature distribution. The program IDARC includes a spread plasticity formulation to capture the variation of the section flexibility, and combine them to determine the element stiffness matrix. In this formulation, the flexibility distribution in the structural elements is assumed to be the linear. The main objective of this study is to evaluate the accuracy of linear flexibility distribution assumed in the spread inelasticity model. For this purpose, nonlinear analysis of two reinforced concrete frames is carried out and the linear flexibility models used in the elements are compared with the real ones. It is shown that the linear flexibility distribution is incorrect assumption in cases of significant gravity load effects and can be lead to incorrect nonlinear responses in some situations.

• Earthquakes and Structures
• /
• 제15권5호
• /
• pp.463-471
• /
• 2018

The virtual forces of the original local flexibility method are restricted to inducing stress on the local parts of a structure. To circumvent this restriction, we developed a pseudo local flexibility (PLFM) method that can successfully detect damage to hyperstatic beam structures using fewer modes. For this study, we further developed the PLFM so that it could detect damage in plate structures. We also devised the theoretical background for the PLFM with non-local virtual forces for plate structures, and both the lateral and rotary degree of freedom (DOF) measurements were considered separately. This study investigates the effects of the number of modes, the actual location that sustained damage, multiple damage locations, and noise in modal parameters for the damage detection results obtained from damaged numerical plates. The results revealed that the PLFM can be used for damage detection, localization, and quantification for plate structures, regardless of the use of the lateral DOF and/or rotary DOF.

• PNF and Movement
• /
• 제8권3호
• /
• pp.55-61
• /
• 2010

Purpose : The purpose of this study was to find out which method was efficient to enhance the flexibility of lower back between PNF(proprioceptive neuromuscular facilitation) and hamstring stretching. Method : subject were 20 young people between the ages 20 and 25. subjects were randomly assigned to one of 2groups; PNF(n=10), static(n=10). respective group received the same stretching does of 3days per week for 4weeks. Trunk flexion forward a measuring instrument and tapeline were performed to measurement the flexibility of lower back at different times(before starting the exercise, 4weeks after starting). Results : The results of the study were as follows: The lower back flexibility was increased significantly in PNF groups. PNF, static groups showed meaningful defference in trunk flexion forward. The finding indicate that PNF may be preferred technique for improving flexibility and that flexibility training results in on increased consistency of flexibility scores.

• Structural Engineering and Mechanics
• /
• 제65권1호
• /
• pp.99-110
• /
• 2018

The focus of this paper is on the elements with stable open cracks. To analyze plane problems, two triangular elements with three and six nodes are formulated using force method. Flexibility matrices of the elements are derived by combining the non-cracked flexibility and the additional one due to crack, which is computed by utilizing the local flexibility method. In order to compute the flexibility matrix of the intact element, a basic coordinate system without rigid body motions is required. In this paper, the basic system origin is located at the crack center and one of its axis coincides with the crack surfaces. This selection makes it possible to formulate elements with inclined cracks. It is obvious that the ability of the suggested elements in calculating accurate natural frequencies for cracked structures, make them applicable for vibration-based crack detection.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2000년도 추계학술대회논문집A
• /
• pp.629-634
• /
• 2000

Dynamic behavior of an automatic dynamic balancer is analyzed by a theoretical approach. Using Lagrange's equation, we derive the non-linear equations of motion for an automatic dynamic balancer equipped in a rotor with the bending flexibility with respect to the rectangular coordinate. Considering the rotor bending flexibility we analyze out-of-plane vibrations as well as in-plane vibrations of the automatic dynamic balaner. The time responses are computed from the non-linear equations by using a time integration method. We also investigate the effect of rotor flexibility on the behavior of the automatic dynamic balancer

• 대한기계학회논문집A
• /
• 제25권7호
• /
• pp.1125-1130
• /
• 2001

Dynamic behaviors of an automatic dynamic balancer are analyzed by a theoretical approach. Using the polar coordinates, the non-linear equations of motion for an automatic dynamic balancer equipped in a rotor with the bending flexibility are derived from Lagrange equation. Based on the non-linear equation, the stability analysis is performed by using the perturbation method. The stability results are verified by computing dynamic response. The time responses are computed from the non-linear equations by using a time integration method. We also investigate the effect of the bending flexibility on the dynamics of the automatic dynamic balancer.

• Structural Engineering and Mechanics
• /
• 제40권1호
• /
• pp.121-148
• /
• 2011

Closed form solutions for equilibrium and flexibility matrices of the Mindlin-Reissner theory based eight-node rectangular plate bending element (MRP8) using Integrated Force Method (IFM) are presented in this paper. Though these closed form solutions of equilibrium and flexibility matrices are applicable to plate bending problems with square/rectangular boundaries, they reduce the computational time significantly and give more exact solutions. Presented closed form solutions are validated by solving large number of standard square/rectangular plate bending benchmark problems for deflections and moments and the results are compared with those of similar displacement-based eight-node quadrilateral plate bending elements available in the literature. The results are also compared with the exact solutions.

• Smart Structures and Systems
• /
• 제23권1호
• /
• pp.15-29
• /
• 2019

This paper addresses the problem of damage detection in suspension bridge hangers, with an emphasis on the modal flexibility method. It aims at evaluating the capability and the accuracy of the modal flexibility method to detect and locate single and multiple damages in suspension bridge hangers, with different level of severity and various locations. The study is conducted numerically and experimentally on a laboratory suspension bridge mock-up. First, the covariance-driven stochastic subspace identification is used to extract the modal parameters of the bridge from experimental data, using only output measurements data from ambient vibration. Then, the method is demonstrated for several damage scenarios and compared against other classical methods, such as: Coordinate Modal Assurance Criterion (COMAC), Enhanced Coordinate Modal Assurance Criterion (ECOMAC), Mode Shape Curvature (MSC) and Modal Strain Energy (MSE). The paper demonstrates the relative merits and shortcomings of these methods which play a significant role in the damage detection ofsuspension bridges.

• Smart Structures and Systems
• /
• 제19권4호
• /
• pp.393-402
• /
• 2017

Many vibration-based global damage detection methods attempt to extract modal parameters from vibration signals as the main structural features to detect damage. The local flexibility method is one promising method that requires only the first few fundamental modes to detect not only the location but also the extent of damage. Generally, the mode shapes in the lateral degree of freedom are extracted from lateral vibration signals and then used to detect damage for a beam structure. In this study, a new approach which employs the mode shapes in the rotary degree of freedom obtained from the macro-strain vibration signals to detect damage of a beam structure is proposed. In order to facilitate the application of mode shapes in the rotary degree of freedom for beam structures, the local flexibility method is modified and utilized. The proposed rotary approach is verified by numerical and experimental studies of simply supported beams. The results illustrate potential feasibility of the proposed new idea. Compared to the method that uses lateral measurements, the proposed rotary approach seems more robust to noise in the numerical cases considered. The sensor configuration could also be more flexible and customized for a beam structure. Primarily, the proposed approach seems more sensitive to damage when the damage is close to the supports of simply supported beams.

• 대한통합의학회지
• /
• 제4권1호
• /
• pp.73-83
• /
• 2016

PURPOSE : The purpose of this study to suggest the exercise programs for improving the function and structure by applying the Masan university scoliosis program exercise method and electrical therapy method to the scoliosis patient. METHODS : The subjects were 18 patients who were diagnosed with scoliosis. They were randomly assigned either to a Masan university scoliosis program exercise group (n=11) that received Masan university scoliosis program exercise program or to a electrical therapy group (n=7). Flexibility, static balance, dynamic balance, and spinal angles were measured by using one leg standing with closed eyes, functional reach test, and Cobb's angle, respectively. The chest expansion were calculated using differences of chest circumference between maximum inspiration and maximum expiration. RESULT : Masan university scoliosis program group before and after the intervention there was a difference in the static balance, spine angle(p<.05). Masan university scoliosis program group before and after the intervention there was a difference in the flexibility, static balance, spine angle, chest expansion (p<.05). CONCLUSION : These results revealed that Masan university scoliosis program exercise program improved flexibility, static standing balance, spine angle, used as scoliosis management and intervention. Therefore, it is expected to be used as a method for the treatment and prevention in the process of rehabilitation of patients with scoliosis.